The primary attachment system used today for lenses is a standard, full circumferential eyeglass frame 1 (FIGS. 1 and 2), either of plastic or metal. The rim 2 surrounds the lens 4, holding it in place. The lens 4 itself will typically have a ridge 6 around the full circumference to allow for the holding of the lens 4 in place (FIGS. 1 and 2). This system has been in place for hundreds of years and represents the basic state of the art.
Another system which has been in place for many years is the "three piece" fixation system. In this form, the eyeglass frame is actually in three pieces with "fingers" extending into the lens into which holes have been drilled and screws affixed (FIGS. 3 and 4). This also has been used for hundreds of years and dates back to some of the earliest eyeglass uses. In addition to the traditional three piece with screws through the lens, a more recent adaptation is that by Air Titanium whereby folded metal rods are inserted through holes in the lens and the opening tension produced by the oversize, bent rods fixes the lens and frame, without the use of screws. This system, however, while reversible, does not provide sufficient structural integrity, and requires intrusion into the lens.
A newer connection system is that of a "half rim" 24 (FIGS. 5 and 6) where structural material is used such as in a full circumferential metal rim, but only through part of the frame. The remainder of the lens is supported through a cord 26, or cable, typically of nylon, which, when put in tension, holds the lens 28 in place by virtue of its fitting in a groove 30 in the lens (FIGS. 5 and 6). An example of this is the Essilor "rimless" frame, which patent issued around 1970.
Other lens systems have been proposed, which include permanently fixing the frame to the lens with pieces such as glue or epoxy. Those have not found significant applications because of their inability to be replaced, requiring full replacement of both the lens and the frame.
A newer method of attachment is described in U.S. Pat. No. 4,895,438 which discloses the use of shape memory 32 alloys to grab onto lens 34, thus providing a reversible positive connection without rims, cords, or screws (FIGS. 7 and 8).